The present invention relates in general to power supplies for reproduction apparatus corona chargers, and more particularly to a bipolar-duty cycle controllable DC corona power supply wherein simulation of AC charging is accomplished by using two DC power supplies acting in tandem to produce the alternate portions of the AC cycle.
In typical commercial electrostatographic reproduction apparatus (copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric member). Pigmented marking particles attracted to the latent image charge pattern to develop such image on the dielectric member. A receiver member is then brought into contact with the dielectric member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
Such reproduction apparatus frequently utilize a corona charger with a grid to apply the initial uniform charge to the photoconductor. The power supply to the gridded corona charger may provide either an AC or DC waveform. Power supplies of the respective types providing either of these waveforms have certain advantages to recommend their use in reproduction apparatus. An AC waveform power supply provides longevity of the associated charger to maintain a uniform charge, and results in the charger exhibiting a high resistance to airborne contaminants. However a DC waveform power supply operates at relatively lower peak voltages, thus reducing arcing and high voltage breakdown. It eliminates the need for large AC transformer (which produces a substantial quantity of heat, is prone to high voltage breakdown, and is substantial in size), is lower in cost and has a higher overall reliability.